Economy Conversion

[BobfromSWOhio]

I have a mid-80's Grady-White 204c (20'4" and 2700#) which I believe is a semi-V hull configuration. Is it possible to use a low HP engine to sacrifice speed and gain economy? I would be happy with trawler like speeds if I could vastly increase mpg. With her type hull will she be more economical at slow planing speeds or even slower displacement speeds? Any idea of minimum HP needed to get her on plane, All (reasonable) suggestions welcome.

 

[Solittle]

Re: Economy Conversion

I'm goin to go the wild guess route:

Displacement speeds: 25-40 hp
Slow planing: 115-140 hp
Good performance: Any V-6

 

[southkogs]

Re: Economy Conversion

How far off the throttle can you back off at plane? I try to run at the point just before the hull comes off plane (typically). I can't imagine that a displacement speed would be more efficient to run at. I'd also be concerned about the trade off trying to fight the way up on plane.

Whatcha' got on it now?

 

[Bondo]

Re: Economy Conversion

I have a mid-80's Grady-White 204c (20'4" and 2700#) which I believe is a semi-V hull configuration. Is it possible to use a low HP engine to sacrifice speed and gain economy? I would be happy with trawler like speeds if I could vastly increase mpg. With her type hull will she be more economical at slow planing speeds or even slower displacement speeds? Any idea of minimum HP needed to get her on plane, All (reasonable) suggestions welcome.

Ayuh,.... Welcome Aboard,....

Just run what you've got at 1000 rpms or less, 'n you'll get yer unbelievable fuel economy.....

 

[Bob's Garage]

Re: Economy Conversion

Boats are not automobiles, smaller engines on a large boat equals poor economy and performance. Get the largest engine the boat is designed to handle and run it at a lower cruising speed. Just because you can doesn't mean you have to run at WOT.

It is a misconception that a boat with a small engine (smaller than it is designed for) is more economical. The engine is having to work harder, at a higher rpm which shortens it's life, causes eventual dissatisfaction with the boat, and reduces the resale value and marketability of the boat.

Also, a deep "V" or semi "V" hull is not intended to perform at maximum efficiency at displacement speed, and their handling is negatively effected. If you want displacement speed efficiency get the trawler but be prepared form the trade off.

 

[BobfromSWOhio]

Re: Economy Conversion

Thanks all. Really appreciated.

 

[Bob_VT]

Re: Economy Conversion

What motor do you have? Are you running trim tabs?

 

[ewenm]

Re: Economy Conversion

i was forced to do this in my previous boat, twin 4.3 efi,s when one motor died due to dead sensor in distributor, so a one hour trip became a three hour journey at 6 knots, and other than fighting 32 feet without power steering we got Awesome economy